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WO1999038020A1 - Convertisseur impedance-tension - Google Patents

Convertisseur impedance-tension Download PDF

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Publication number
WO1999038020A1
WO1999038020A1 PCT/JP1999/000098 JP9900098W WO9938020A1 WO 1999038020 A1 WO1999038020 A1 WO 1999038020A1 JP 9900098 W JP9900098 W JP 9900098W WO 9938020 A1 WO9938020 A1 WO 9938020A1
Authority
WO
WIPO (PCT)
Prior art keywords
impedance
input terminal
operational amplifier
inverting input
target
Prior art date
Application number
PCT/JP1999/000098
Other languages
English (en)
Inventor
Tatsuo Hiroshima
Koichi Nakano
Muneo Harada
Toshiyuki Matsumoto
Yoshihiro Hirota
Original Assignee
Sumitomo Metal Industries, Ltd.
Hokuto Electronics, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sumitomo Metal Industries, Ltd., Hokuto Electronics, Inc. filed Critical Sumitomo Metal Industries, Ltd.
Priority to KR1019997008619A priority Critical patent/KR100558379B1/ko
Priority to IL13189199A priority patent/IL131891A0/xx
Priority to DE69931104T priority patent/DE69931104T2/de
Priority to EP99900308A priority patent/EP0970386B8/fr
Priority to AU18900/99A priority patent/AU729354B2/en
Priority to US09/381,673 priority patent/US6335642B1/en
Publication of WO1999038020A1 publication Critical patent/WO1999038020A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
    • G01R27/2605—Measuring capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables

Definitions

  • the present invention relates to an impedance-to- voltage converter (hereinafter referred to as "a Z/V converter”) for outputting a voltage corresponding to an impedance value of a target to be detected using an operational amplifier. More particularly, the present invention relates to a Z/V converter using an operational amplifier, which can remove the influence of stray capacitances on a signal line, and thereby can produce a voltage corresponding to an impedance of a target to be detected all the more accurately.
  • BACKGROUND ART Fig. 1 schematically illustrates a prior art electrostatic capacitance-to-voltage converter described in Japanese Patent Public Disclosure (Laid-open) No. 61-14578.
  • This electrostatic capacitance-to-voltage converter has been proposed to solve the following problems caused by stray capacitances on a cable connecting an unknown electrostatic capacitance to an input terminal of an operational amplifier. That is , the stray capacitances on the cable are superimposed on the electrostatic capacitance to be detected and the values of the stray capacitances vary due to movements, bending and so on of the cable, so that the impedance value of the electrostatic capacitance may not be converted into a correctly-associated voltage.
  • the present invention has been proposed to solve such inherent problems in a prior art as shown in Fig. 1. Therefore, it is an object of the present invention to provide an impedance-to-voltage converter (Z/V converter) which is capable of highly accurately converting an impedance value Z of a target or a component to be detected into a voltage V without any influence of stray capacitances occurring between a signal line and a shielding means, even if the impedance value Z is relatively small.
  • Z/V converter impedance-to-voltage converter
  • an impedance/voltage (Z/V) converter for converting an impedance of a target to a voltage
  • an operational amplifier having a feedback impedance circuit connected between an output terminal and an inverting input terminal thereof, a signal line having one end connected to the inverting input terminal of the operational amplifier and the other end connected to one electrode of a target impedance, alternate current (AC) signal generator connected to a non-inverting input terminal of the operational amplifier, and at least one shields comprising at least one shielding layer which surrounds at least a portion of the signal line and is connected to the non-inverting input terminal of the operational amplifier and the AC signal generator, wherein the inverting and non-inverting terminals are imaginal-short, whereby the operational amplifier outputs from its output terminal a voltage corresponding to the impedance value of the target .
  • the shielding layer preferably comprises a mesh structure or tube structure.
  • the shield further includes a second shielding layer surrounding the outer surface of the first shielding layer, which comprises a mesh structure or tube structure and is connected to the non-inverting input terminal of the operational amplifier and the AC signal generator or to a reference voltage.
  • the impedance of the target and the feedback impedance circuit both have the same character comprising a resistive, capacitive or inductive one or any combination thereof. In such a case, S/N ratio of the apparatus may be improved.
  • Other combinations can be acceptable and when the impedance of the target is an electrostatic capacitance, and the feedback impedance circuit is a resistance, it is easy to integrate the operational amplifier and the feedback impedance circuit in a chip.
  • Fig. 1 is a circuit diagram illustrating an electrostatic capacitance-to-voltage converter of a prior art
  • Fig. 2 shows a circuit diagram of a first embodiment of an impedance-to-voltage (Z/V) converter according to the present invention
  • Fig. 3 is a graph representing a tested example of the relationship between a capacitance Cx and an output voltage Vo where an impedance of a target to be detected is the capacitance;
  • Fig. 4 illustrates a circuit diagram of a second embodiment of a Z/V converter according to the present invention
  • Figs. 5(A) and 5(B) are graphs showing the results of noise influence tested example using the first and second embodiments ;
  • Fig. 6 shows a circuit diagram of a third embodiment of a Z/V converter according to the present invention.
  • Fig. 7 is a circuit diagram of the first embodiment when the target has an electrostatic capacitance as its impedance and the feedback impedance circuit consists of a resistor.
  • Fig. 2 is a circuit diagram schematically illustrating a first embodiment of the Z/V converter according to the present invention.
  • the numeral 1 denotes an operational amplifier having a voltage gain extremely much larger than a closed loop gain.
  • a feedback impedance circuit 3 is connected between an output terminal 2 and an inverting input terminal ( - ) of the operational amplifier 1 to form a negative feedback loop across the operational amplifier 1.
  • the feedback impedance circuit 3 may be arbitrary impedance component such as a resistor, a capacitor, an inductor or any combination thereof.
  • the operational amplifier 1 has a non-inverting input terminal (+) connected to an AC signal generator 4 for generating an alternate current (AC) voltage.
  • the inverting input terminal ( - ) of the operational amplifier is also connected to one end of a signal line 5.
  • the other end of the signal line 5 is connected to a sensing electrode 6 X of a target or target component 6, an impedance value of which is measured.
  • the target may be arbitrary impedance component such as a resistor, a capacitor, an inductor or any combination thereof.
  • the other electrode 6 2 of the target 6 is grounded, or clamped to a constant DC voltage (not equal to the ground level), or kept an open state or non-connection state.
  • the second electrode 6 2 might be applied with an AC bias, more complicated mathematical analysis would be required for an output voltage of the operational amplifier 1.
  • a shield 7 consisting of a shielding layer is wrapped round the signal line 5 in order to prevent external unwanted signals such as noise from being introduced into the signal line 5.
  • the shield 7 is not grounded but is connected to the non-inverting input terminal (+) of the operational amplifier 1 and hence the AC signal generator 4. Since the operational amplifier 1 is provided with the negative feedback by means of the circuit including the feedback impedance circuit 3 and it has a voltage gain which is far larger than its closed loop gain, the inverting input terminal (-) and the non-inverting input terminal (+) of the operational amplifier 1 are in an imaginal-short state, so that a voltage difference therebetween is substantially zero.
  • the signal line 5 and the shield 7 respectively connected to the inverting and non-inverting input terminals have the same voltage, so that it is possible to cancel any stray capacitances which may take place between the signal line 5 and the shield 7. This is true irrespective of the length of the signal line 5, and this is also true whether the signal line 5 is moved, bent, or folded back.
  • the AC voltage output from the AC signal generator 4 is Vi
  • the unknown impedance value of the target 6 is Zx
  • a current flowing through the target 6 is i 1#
  • a known impedance value of the feedback impedance circuit 3 is Zf
  • a current flowing through the feedback impedance circuit 3 is i 2
  • a voltage at the inverting input terminal (-) of the operational amplifier 1 is Vm
  • an output voltage of the operational amplifier 1 is Vo.
  • the second electrode 6 2 of the target 6 is grounded.
  • the currents i 1# i 2 are expressed by the following Equations :
  • Equation (1) represents that the operational amplifier 1 outputs an AC voltage Vo which varies dependently on the impedance value Zx.
  • a block 8 illustrated by one-dot chain lines including the signal line 5, the shield 7, the AC signal generator 4, the operational amplifier 1 connected to the signal line and the feedback impedance circuit 3 constitutes a Z/V converter for converting the impedance value Zx of the target component 6 connected to the other terminal of the signal line 5 into a voltage Vo corresponding thereto.
  • the output voltage Vo of the operational amplifier 1 does not include any term relating to the stray capacitances occurring between the signal line 5 and the shield 7. Therefore, even if the impedance value Zx of the target 6 is small, the voltage Vo from the operational amplifier 1 corresponds only to the small impedance Zx.
  • the output voltage Vo of the operational amplifier 1 is represented by the Expression (1), where the value Zf of the feedback impedance circuit 3 and
  • the frequency and amplitude of the AC signal Vi are known. Further, the output Vo of the operational amplifier 1 has the same frequency as the AC signal voltage Vi and its amplitude can be obtained by detecting the peaks of the output wave of the amplifier 1. Therefore, by solving the Equation (1), the impedance value Zx can be calculated therefrom.
  • the Vo varies linearly to the Cx as apparent from the Equation ( 1 ) .
  • the relationship between the Cx and an amplitude of the Vo has been obtained as a graph shown in Fig. 3.
  • the impedance value Zx can be calculated using the Vdd.
  • the circuit generating the DC voltage Vdd corresponding to the output voltage Vo can be provided by any AC-DC converter such as a rectifier and smoothing circuit. If necessary, such an AC-DC conversion may be executed after an amplification of the voltage Vo.
  • the shield 7 may be a tube-type shielding means.
  • the shield 7 may be formed in a single layer mesh structure which comprises knitted narrow metal strips in order to provide a flexible coaxial cable comprising of the signal line 5 and the shield 7.
  • a high frequency signal if generated from the AC signal generator 4, would leak from the signal line 5 through micro-holes of the mesh structure 7, resulting in possibly affecting the AC output voltage Vo.
  • high frequency external noise may also be introduced into the signal line 5 through the micro-holes, in which case the AC output voltage Vo would be affected by the external noise.
  • the output voltage Vo from the operational amplifier 1 may vary.
  • Fig. 4 illustrates a second embodiment of a Z/V converter according to the present invention which can perform Z/V conversion in a high accuracy, even if a shield means is made in a mesh structure to provide flexibility.
  • the same components as those in the first embodiment in Fig. 2 are designated by the same reference numerals.
  • the second embodiment differs from the first one in that a shield means is made in a double-layer mesh structure comprising an inner shield (a first shielding layer) 7 X and an outer shield (a second shielding layer) 7 2 , both of which are connected to a non-inverting input terminal of an operational amplifier 1.
  • the shield means since the shield means has the double-layer mesh structure (the inner and outer shields l and 7 2 ), holes of thereof have smaller diameters as compared with those of the single-layer mesh structure, so that even if a high frequency signal is generated from an AC signal generator 4, the leaking electric field of the high frequency signal from a signal line 5 into the shields 7 1# 7 2 is reduced. Further, the influence of external noise is also reduced. Therefore, it is possible to produce an output voltage Vo correctly corresponding to an impedance value Zx to be detected.
  • Tl, T2 and T3 represent time periods during which the cable was touched by hand.
  • Fig. 6 illustrates a third embodiment of a Z/V converter according to the present invention. While the third embodiment is similar to the second one in that a double-layer mesh structure is employed for a shielding means and an inner shielding means l ⁇ is connected to a non- inverting input terminal of an operational amplifier 1 , the third embodiment does differ from the second embodiment in that an outer shield 7 2 is grounded.
  • the grounded outer shield 7 2 in the third embodiment may cause an interlayer capacitance, i.e., parasitic capacitance between the inner shield l x and the outer shield 7 2 , which may have 1000 pF/m or more.
  • the parasitic capacitance becomes larger as a coaxial cable (a signal line 5 and the inner and outer shields 7 1 7 2 ) is longer.
  • a higher frequency signal from an AC signal generator 4 causes a reduction in impedance of the parasitic
  • the third embodiment is preferably applied when a sensing electrode 6 X is positioned relatively close to the operational amplifier 1 and connected thereto with a relatively short coaxial cable, or when the frequency of a signal from the AC signal generator 4 is relatively low.
  • the shield 7 it is preferable to shield the whole signal line 5 by the shield 7 or the inner and outer shields l x and 7 2 . It is more preferable to shield the whole apparatus excluding the sensing electrode 6 ⁇
  • the target 6 may be arbitrary impedance component such as a resistor, a capacitor, an inductor or any combination thereof .
  • the first to third embodiments provide capacitance-to- voltage (C/V) converters and therefore constitute capacitive sensors.
  • an electrode 6 2 of the capacitance element Cx is grounded, set at an appropriate bias voltage, or left in space.
  • Capacitive sensors to which the present invention may be applicable include arbitrary capacitive sensors such as acceleration sensor, seismometer, pressure sensor, displacement sensor, displacement meter, proximity sensor, touch sensor, ion sensor, humidity sensor, rain drop sensor, snow sensor, lightning sensor, alignment sensor,
  • the present invention may also be applied to a printed circuit board tester. Specifically, for a printed circuit board determination is made as to whether it is usable or not in view of the magnitude, uniformity and so on of electrostatic capacitances parasitic on the board.
  • a voltage corresponding to the electrostatic capacitance value Cx at the portion can be produced from the operational amplifier 1 , thereby making it possible to determine whether the board is usable or not.
  • an electrostatic capacitance detector for deriving the capacitance value Cx can be implemented by combining the block 9 with a means for processing the output voltage Vo.
  • a capacitor is employed as the feedback impedance circuit 3 when the target 6 is a
  • a resistor may be employed as the feedback impedance element 3 when the target 6 is a capacitive component Cx.
  • the use of a resistor as the feedback impedance circuit facilitates the formation of the operational amplifier 1 and the feedback resistor 3 into one chip.
  • the output voltage Vo can be expressed from the equation (1) as follows:
  • a parallel circuit of a resistor and a capacitor or the like may be employed as the feedback impedance circuit 3. Further alternatively, any arbitrary combinations are possible.
  • the 15 position of the feedback impedance circuit 3 may be replaced with that of the target 6 to be detected. That is, the target 6 may be connected between the inverting input terminal and the output terminal of the operational amplifier 1 , while a known impedance circuit may be connected to the end of the signal line 5. In this case, shielding means need to be provided to cover two lines for connecting two sensing electrodes of the target 6 to the inverting input terminal and the output terminal of the operational amplifier 1.
  • the feedback impedance circuit 3 may also be an unknown impedance component , as well as the target 6.
  • a two-axis acceleration sensor is contemplated.
  • the two-axis acceleration sensor operates such that as the impedance of one sensor becomes larger in response to increasing acceleration, the impedance of the other sensor becomes smaller. Therefore, the value of the impedance ratio largely varies even if the respective impedances exhibit small amounts of changes. Since the AC output voltage Vo varies correspondingly to the impedance ratio which largely varies even with such slight changes in the respective impedance value, it is possible to significantly improve the detection sensitivity of the two-axis acceleration sensor.
  • the feedback impedance circuit or element 3 may also be an unknown resistive component.
  • a variant Y such as pressure, temperature or the like
  • the value of the ratio Zf/Zx varies dependently on the variant Y, thus producing an output voltage Vo an amplitude of which varies in response to the variant Y.
  • some combination of such impedance components may allow the output voltage Vo to linearly vary its amplitude in response to the variant Y.
  • the output voltage Vo may be made to non-linearly vary.
  • the present invention as described above, can produce positive effects as follows: (1) Since a signal line connected to an impedance component or target component under detection and a shield surrounding the same are at the same voltage due to the imaginal-short of an operational amplifier, it is possible to produce a voltage which depends only on an impedance value of the target component without any influence of a parasitic capacitance possibly formed between the signal line and shield. Therefore, highly accurate Z/V conversion can be achieved even if only a very small impedance value is to be detected.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Amplifiers (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

L'invention concerne un convertisseur impédance-tension permettant de convertir en tension l'impédance d'un dispositif cible. Ce convertisseur comprend un amplificateur opérationnel, un câble coaxial constitué d'une ligne de signal et d'un ou plusieurs éléments de blindage, et un générateur de signaux en courant alternatif. Un circuit à impédance de contre-réaction est établi entre des bornes de sortie et d'inversion de l'amplificateur opérationnel, moyennant quoi une borne non inverseuse et la borne d'inversion sont à l'état de court-circuit fictif. Une extrémité de la ligne de signal est reliée à la borne d'entrée inverseuse de l'amplificateur opérationnel, et l'autre extrémité est reliée à une électrode du dispositif cible. Le générateur de signaux en courant alternatif est relié à la borne d'entrée non inverseuse de l'amplificateur opérationnel. Le ou les éléments de blindage comprennent au moins une couche de blindage entourant la ligne de signal, et ils sont reliés à la borne d'entrée non inverseuse de l'amplificateur opérationnel, moyennant quoi la ligne de signal et la couche de blindage ont la même tension suite à l'état de court-circuit fictif des bornes d'entrée de l'amplificateur opérationnel. Il en résulte une diminution du bruit sur la ligne de signal.
PCT/JP1999/000098 1998-01-23 1999-01-14 Convertisseur impedance-tension WO1999038020A1 (fr)

Priority Applications (6)

Application Number Priority Date Filing Date Title
KR1019997008619A KR100558379B1 (ko) 1998-01-23 1999-01-14 임피던스-전압 변환기
IL13189199A IL131891A0 (en) 1998-01-23 1999-01-14 Impedance-to-voltage converter
DE69931104T DE69931104T2 (de) 1998-01-23 1999-01-14 Impedanz-spannungswandler
EP99900308A EP0970386B8 (fr) 1998-01-23 1999-01-14 Convertisseur impedance-tension
AU18900/99A AU729354B2 (en) 1998-01-23 1999-01-14 Impedance-to-voltage converter
US09/381,673 US6335642B1 (en) 1998-01-23 1999-01-14 Impedance-to-voltage converter

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
JP1158198 1998-01-23
JP2624098 1998-02-06
JP10/11581 1998-12-09
JP10/350021 1998-12-09
JP10/26240 1998-12-09
JP35002198 1998-12-09

Publications (1)

Publication Number Publication Date
WO1999038020A1 true WO1999038020A1 (fr) 1999-07-29

Family

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Family Applications (2)

Application Number Title Priority Date Filing Date
PCT/JP1999/000098 WO1999038020A1 (fr) 1998-01-23 1999-01-14 Convertisseur impedance-tension
PCT/JP1999/000229 WO1999038019A1 (fr) 1998-01-23 1999-01-22 Convertisseur capacite statique-tension et procede de conversion

Family Applications After (1)

Application Number Title Priority Date Filing Date
PCT/JP1999/000229 WO1999038019A1 (fr) 1998-01-23 1999-01-22 Convertisseur capacite statique-tension et procede de conversion

Country Status (11)

Country Link
US (2) US6335642B1 (fr)
EP (2) EP0970386B8 (fr)
JP (1) JP3302377B2 (fr)
KR (2) KR100558379B1 (fr)
CN (2) CN1255975A (fr)
AU (2) AU729354B2 (fr)
DE (2) DE69931104T2 (fr)
DK (2) DK0970386T3 (fr)
IL (2) IL131891A0 (fr)
TW (1) TW448302B (fr)
WO (2) WO1999038020A1 (fr)

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US6335642B1 (en) 2002-01-01
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DE69931217D1 (de) 2006-06-14
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CN1255974A (zh) 2000-06-07
EP0970386B8 (fr) 2006-06-21
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US6331780B1 (en) 2001-12-18
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KR20010005556A (ko) 2001-01-15

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